1. Field of the Invention
The present invention relates to the utilization of a multilayered cap barrier layer that has a low composite dielectric constant (k<4.0) and has barrier properties to metal diffusion and air permeation. More particularly, the present invention relates to the use of the multilayered cap barrier layer in metal interconnect structures that are part of integrated circuits and microelectronic devices. The primary advantage that is provided by the present invention is the reduction in the capacitance between conducting metal features, e.g., copper lines, that results in an enhancement in overall chip performance. Methods for the utilization, compositions of matter, and structures that implement the barrier films are also described.
2. Background Art
The utilization of materials that serve as diffusion barriers to metal in metal interconnect structures, that are part of integrated circuits and microelectronic devices, is typically required to generate reliable devices as low-k interlayer dielectrics do not prohibit metal diffusion. The placement of these materials in the interconnect structure can differ and will be dependent upon their qualities and the means in which they are deposited and processed. Both barrier layers comprised of metal and dielectrics are commonly utilized in interconnect structures.
Diffusion barrier layers, comprised of metal and metal containing materials including, for example, tantalum, tungsten, ruthenium, tantalum nitride, titanium nitride, TiSiN, etc., often serve as liners whereby they form a conformal interface with metal conducting structures. Normally, these materials are deposited by chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition, (ALD), sputtering, thermal evaporation, and other related approaches. To utilize these materials as barrier layers, the metal barrier layers must be conformal to conducting metal lines and cannot be placed as blanket layers that would serve as conducting pathways between metal lines. One limiting criteria for these barrier layers is that their contribution to the resistivity of conducting metal lines must not be excessively high; otherwise, the increase in the total resistance of the metal conducting structures would result in reduced performance.
Diffusion barrier layers comprised of dielectrics including, for example, silicon nitrides, silicon carbides, and silicon carbonitrides, are also utilized in microelectronic devices. These materials are normally deposited by chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PECVD) approaches and can be deposited as continuous films, e.g., as cap barrier layers. Unlike diffusion barrier layers comprised of metal, the dielectric layers can be deposited as blanket films and can be placed between conducting metal lines. In doing so, these dielectric layers contribute to the capacitance between metal lines. A limiting constraint of these systems is their relatively high dielectric constants (k=4.5-7) that result in a substantial increase in the effective dielectric constant between metal lines and leads to reduced device performance. Decreasing the film thickness of these barrier layers can lead to reductions in the effective dielectric constant; however, insufficiently thick layers may not be reliable and nevertheless may have significant contributions to the effective dielectric constant.
Barrier layer films that are generated by spin-coating, or other solvent based approaches, that prohibit copper diffusion have also been proposed. These systems can be polymers that may be cured at elevated temperatures to produce rigid, crosslinked systems that are thermally stable to temperatures in excess of 400° C. A primary advantage of many of these systems is the low dielectric constant that these materials exhibit; dielectric constants of 2.6 have been measured. Examples of such systems include: polysilazanes, polycarbosilanes, polysilsesquiazanes, polycarbosilazanes, etc.
In addition to copper diffusion barrier properties, barrier properties to air permeation is highly desirable for barrier layer films. Air permeation through barrier layer films can adversely lead to oxidation of conducting metal features and result in reduced reliability and/or performance. Some dielectric copper diffusion barriers deposited by CVD and related approaches have been observed to display air barrier properties due to their high density. However, many of the low-k copper diffusion barriers applied by solvent based approaches do not serve as a barrier to air permeation due to their relatively open structure which may contain a significant portion of voids or free volume.